This is the national phase of PCT/EP98/03590, filed Jun. 15, 1998, now WO99/00395.
German application P 196 35 656.3 relates to a process for preparing phosphonium phenolates which is characterised in that phosphonium halides are reacted with phenols in a mixture of water, aqueous caustic alkali solution and inert solvent for between 2 minutes and 4 hours at temperatures from 0xc2x0 C. to 40xc2x0 C. and at pressures from 1 bar to 20 bar in the molar ratio 0.5 mol to 2 mol of phenol, preferably 0.7 to 1.3 moles of phenol, per mole of phosphonium halide.
CH2Cl2 and C6H5Cl are mentioned as inert solvents in that document.
On page 4 of the German patent application P 196 35 656.3 it is also shown that phosphonium salts are converted into the corresponding phosphine oxide by bases. This is demonstrated in example A of this application, wherein a pH of about 14 is used. (See also comparison example in this application and German application P 19723524.7, which was filed on May 6, 1997 with intermediate priority date over P 19635656.3.)
During further development of this process it has now been found that alcohols which are sparingly soluble in water, that is up to a maximum of 15 wt. % solubility, may be used instead of inert solvents.
It was also found, surprisingly, that the formation of phosphine oxides is suppressed if the reaction is performed in alkaline solution, even without an alcohol, at a pH between 9.5 and 11, preferably between 9.5 and 10.5 and in particular between 10.0 and 10.5.
The present invention, therefore, provides a process for preparing phosphonium phenolates from phosphonium halides and phenols in aqueous alkaline solution at temperatures from 0 to 55xc2x0 C., preferably 15 to 50xc2x0 C., which is characterised in that the reaction is performed in the molar ratio of phenol to phosphonium halide between 2:1 and 10:1, preferably between 4.5:1 and 6:1 and in particular 5:1, at a pH of 9.5 to 11, preferably 9.5 to 10.5 and in particular 10 to 10.5 and optionally in the presence of alcohols in amounts of 50 wt. % to 200 wt. %, preferably 66 wt. % to 125 wt. %, with respect to the weight of the aqueous phase, wherein the alcohols have a solubility in pure water of at most 15 wt. %.
Phosphonium phenolates can be prepared in high yields using the process according to the invention.
Phosphonium phenolates are suitable in particular as catalysts for esterification and transesterification, in particular to prepare polycarbonates by the melt transesterification process (see U.S. Pat. No. 3,442,854).
The solubility of alcohols in water is known from the literature.
Suitable alcohols according to the invention are aliphatic alcohols with the formula CnH2n+1OH in which n is an integer from 3 to 10 inclusive.
Suitable alcohols according to the invention are also cycloaliphatic alcohols with the formula CnH2nxe2x88x921OH in which n is an integer from 5 to 10 inclusive.
Preferred aliphatic alcohols are (iso)butanols, pentanols and hexanols, in particular isobutanol.
Preferred cycloaliphatic alcohols are cyclopentanol, cycloheptanol and cyclooctanol, in particular cyclohexanol.
The ratio by weight of water to alcohol is between 2:1 and 0.5:1, preferably between 1.5:1 and 0.8:1.
The sparingly soluble alcohols to be used according to the invention are added to facilitate the working-up procedure, since the phenol/alcohol mixture has a lower density than the aqueous solution and thus the organic phase is above the aqueous phase. The aqueous phase can thus be drawn off from below. The organic phase which contains the phenolate can then be washed with deionised water in the same separating vessel and the wash water can again be drawn off from below.
If an alcohol is not added, then the salt-containing aqueous solution is the only phase more dense than the organic phase and it can thus be drawn off from below. During the subsequent wash procedures using deionised water there is a phase inversion, the organic phase is then the denser phase and therefore is found below the aqueous phase. This working-up procedure has proven to be more costly in so far as a second processing vessel is required.
Phosphonium halides of the formula (I) are particularly suitable for the reaction according to the invention 
in which
R1 to R4 are identical or different, and each represents a C1-C12 alkyl, C5-C6 cycloalkyl, C7-C12 aralkyl or C6-C14 aryl group,
and
X(xe2x88x92) represents a halide ion, preferably F(xe2x88x92), Cl(xe2x88x92) or Br(xe2x88x92) and n is 1 or 2, wherein n is 2 when R4 represents a C2-C12 alkylene group.
The groups R1 to R4 are identical or different, and each, preferably, represents a C6-C14 aryl group or the groups R1 to R3 each represent a C6-C14 aryl group and R4 represents a C2-C12 alkylene group.
These types of phosphonium halides and methods for their preparation are known (see for example xe2x80x9cHouben-Weyl, Methoden der organischen Chemiexe2x80x9d volume XII/1, pages 79 et seq and Worrall, J. Amer. Chem. Soc, 52 (1930), pages 293 et seq).
These compounds (I) are produced during the reaction of trialkyl or triarylphosphines, for example triphenyl phosphine, with halogenated aromatic compounds or halogenated alkyl compounds, e.g. benzyl bromide, in the presence of metal salts (Friedel-Crafts alkylation) or in the presence of Grignard reagents and cobalt(II) chloride.
Preferred phenols are those of the formula (II) 
in which
R5 to R7, independently of each other, represent H, C1-C12 alkyl, C5-C6 cycloalkyl, C7-C12 arylalkyl and C6-C14 aryl groups; R5 to R7 are preferably hydrogen atoms.
These types of phenols are known from the literature.
Preferred phosphonium phenolates are thus those of the formula (III) 
in which the groups R1 to R7 correspond to those in formulae (I) and (II) and n is again 1 or 2.
Deionised water or distilled water is preferably used for preparing the aqueous alkaline phase.
The pH can be adjusted to 9.5 to 11.0, preferably 9.5 to 10.5, in particular 10.0 to 10.5, using a caustic alkali solution, preferably caustic soda solution or caustic potash solution, taking into account the buffering effect of phenol/Na phenolate.
The process according to the invention may be performed continuously or batchwise, wherein a batchwise mode of operation is preferred.
According to a preferred mode of operation, phenol, phosphonium halide and alkanol as solution are initially introduced and water is then added. The pH is adjusted to 9.5 to 11.0, preferably 9.5 to 10.5, in particular 10.0 to 10.5 by adding caustic alkali solution, optionally with cooling. The temperature is maintained at 0 to 55xc2x0 C., preferably 15 to 50xc2x0 C., preferably with vigorous mixing of the reaction components. The reaction should be allowed to continue for a period of up to 2 hours, preferably up to 1 hour.
The phosphonium phenolate prepared according to the invention is preferably isolated, when using an alcohol which is sparingly soluble in water, by separating the aqueous phase from the organic phase, extracting the organic phase at least once, preferably 3 times, with deionised water or distilled water, then removing the alcohol, for example by distillation, and drying the reaction product after removing the phenol. If the phosphonium phenolate is produced in crystalline form during the two-phase boundary reaction according to the invention, these crystals may be recovered using conventional working-up procedures, inter alia by washing with deionised water or distilled water, optionally after recrystallising and drying.
If a sparingly soluble alcohol is not used, the precipitated crystals are extracted with deionised or distilled water.
Quaternary phosphonium phenols prepared according to the invention are in particular 
Use of the phosphonium phenolates obtained according to the invention to prepare aromatic polycarbonates may take place in a manner known per se (see U.S. Pat. No. 3,442,854 loc cit).
As is well known the melt transesterification process uses, for example, aromatic diphenols, esters of diaryl carbonates and optionally branching agents and/or monophenols as starting materials.
The phosphonium phenolates obtained according to the invention are used in this process as catalysts in amounts of 10xe2x88x921 moles to 10xe2x88x928 moles, preferably in amounts of 10xe2x88x923 moles to 10xe2x88x927 moles, per mole of diphenol.
Further details relating to the melt transesterification process are described in the literature (see for example Hermann Schnell, Chemistry and Physics of Polycarbonates, Polymer Reviews, Vol 9, 1964, pages 44 to 51, DE-A 1 031 512, U.S. Pat. Nos. 3,022,272, 5,340,905 and 5,399,659).
Thermoplastic polycarbonates prepared using phosphonium phenolates obtained according to the invention are solvent-free, have an intrinsically pale colour and the final polycarbonate is largely free of unwanted defects.
The polycarbonates prepared in this way may be used on an industrial scale in the form of a very wide variety of moulded articles, in all areas in which thermoplastic polycarbonates have been used hitherto, for instance in electrical engineering components, as lamp covers, as safety shields or as CD material.